Apparatus and method for manufacturing a semiconductor wafer with reduced delamination and peeling

ABSTRACT

A multi-layered semiconductor structure with free areas limiting the placement of test keys. First and second scribe lines intersect to define one corner point of a die. The first and second scribe lines are part of the multilayered structure and at least one layer of the multi-layer structure is a low-k dielectric layer. Free area A 1  is defined on the first scribe line and is defined by the equation A 1 =D 1 ×S 1 , where D 1  is the distance from the corner point of the die toward the main area of the die, and S 1  is the width of the first scribe line. Free area A S  is defined at the intersection of the first scribe line and the second scribe line adjacent the die and is defined by the equation A S =S 1 ×S 2 , where S 2  is the width of the second scribe line.

This application claims the benefit of U.S. Provisional Application No.60/462,969 filed on Apr. 15, 2003, entitled Semiconductor Wafer withFree Areas for Test Key Placement, which application is herebyincorporated herein by reference.

TECHNICAL FIELD

The invention relates to a semiconductor wafer including aninter-metal-dielectric layer of low dielectric constant (low-k), andmore particularly to a design rule for placing test keys on a scribeline. A second embodiment relates to a conductive ring design rule on acorner area of a die. A “free area” that restricts test key placementdefined on the scribe line can prevent delamination or peeling near thedie corners. One or more slots formed in the conductive ring can preventthe low-k layer from being cracked by stresses exerted at the diecorners.

BACKGROUND

IC manufacturers are employing finer circuit widths, low dielectricconstant (low-k) materials, and other technologies to make small andhigh-speed semiconductor devices. Along with these advancements, thechallenges of maintaining yield and throughput have also increased. Asfar as reliability is concerned, the low-k material near die corners hasa crack issue, especially in the sawing process.

A semiconductor wafer typically comprises substantially isolated dies(or chips) separated from each other by scribe lines. Individual dieswithin the wafer contain circuitry, and the dies are separated by sawingand are individually packaged. Alternately, the individual dies may bepackaged in multi-chip modules. In a semiconductor fabrication process,the semiconductor device (e.g., an integrated circuit IC) must becontinuously tested at every step so as to maintain and assure devicequality. Usually, a testing circuit is simultaneously fabricated on thewafer along with the actual devices. A typical testing method providesseveral test keys located on the scribe lines between dies that may beelectrically coupled to an external terminal through a metal pad. Thetest keys are selected to test different properties of the wafer, suchas threshold voltage, saturation current, gate oxide thickness, orleakage current.

In general, the scribe lines are defined in areas of the multi-layerstructure that are without a die pattern and have a width of about 80 to100 μm depending on the dimensions of the dies manufactured in thewafer. In order to prevent cracks induced during wafer sawing frompropagating into the die, each die is usually surrounded by a seal ringof 3 to 10 μm in width. Nevertheless, during wafer manufacture, damageis often introduced because of the scribe lines. Further, when at leastone layer of the multi-layer structure is composed of a metal materialwith a high thermal expansion coefficient, the dimensional variation ofthe layer is sufficient to introduce high-level internal stress into thewafer in the area of the scribe line. Consequently, portions of thewafer around the scribe line suffer damage, such as peeling,delamination, or dielectric fracture. The types of scribe line damagementioned above are usually observed when the multi-layer structureincludes an inter-metal-dielectric layer of low dielectric constant(low-k).

When considering a design rule for placement of test keys on the scribeline, major consideration is that the stress resulting from the sawingprocess causes serious peeling near the test keys at the die corners.This results in delamination at the interface between the multiplelayers at the die corners. Delamination impacts the reliability of thedevice, and contributes to production of stringers (residual materials)that interfere with further processing and testing of the integratedcircuit.

Several solutions have been proposed to solve some of the technicalproblems associated with the manufacture and sawing of semiconductorwafers. According to some approaches, grooves are formed in theinsulating zone by plasma etching. The formation of these grooves stopsmany, but not all, cracks from forming. Therefore, a novel test keydesign rule for preventing delamination or peeling near the die cornersis called for.

A conductive ring provided on the main area of the die is well known forproviding the wiring that supplies the ground potential or power sourcepotential to circuits in the die. It is not uncommon for stresses tocrack a passivation film formed over the die corners during the sealingprocess of a resin mode package. As disclosed in U.S. Pat. No.5,371,411, one solution to this problem is to form a slot or row ofsmall holes in the guard ring. However, it is not believed that an arrayof apertures in the guard ring has been used to prevent a crack ordefect generated in an inter-metal-dielectric layer resulting from a diesawing process as proposed by the present invention. If a low-k materialis used near the guard ring corners, the crack issue becomes moreserious and further reduces reliability. Thus, a novel guard ring designrule at the die corners is also taught by the present invention.

SUMMARY OF THE INVENTION

Accordingly, the present invention provides a “free area” that prohibitsor substantially limits test key placement on the scribe lines in orderto prevent delamination and peeling near the die corners.

The present invention also provides a conductive ring with one or moreslots or rows of holes to prevent the low-k material from being crackedby stresses exerted at the die corners.

In some embodiments of the invention, a multi-layer semiconductor waferstructure defines areas where test key placement is restricted. At leastone layer of the multi-layer structure is a low-k dielectric layer.Depending upon the requirement of the semiconductor design, theserestricted areas may substantially limit or even prohibit the placementof test keys and are referred to herein as “free areas.” Thesemiconductor wafer comprises at least a first and second scribe line.The first scribe line extends along a first direction as part of amulti-layer structure, and the second scribe line extends along a seconddirection of the multi-layer structure. The intersection of the firstscribe line and the second scribe line defines at least one corner pointof a main area of a die. At least one “free area” restricting test keyplacement is defined on the first scribe line adjacent the corner pointof the die, in which the “free area” A₁ is defined by the equation:A₁=D₁×S₁, where D₁ is a first distance from the corner point of the dieextending toward the main area of the die, and S₁ is the width of thefirst scribe line. Another “free area” A_(S) is defined on theintersection of the first scribe line and the second scribe lineadjacent the corner point of the die. The “free area” A_(S) is definedby the equation: A_(S)=S₁×S₂, where S₁ is the width of the first scribeline, and S₂ is the width of the second scribe line.

The low-k dielectric layer has a dielectric constant less thanapproximately 3.5 and preferably less than 3.0, and the “free area” isdefined on at least one layer of the multi-layer structure of the firstscribe line. A few test keys may be allowed in the “free areas” locatedon the first scribe line or the second scribe line. A measurement ratioR₁ is defined by the equation R₁=M₁/A₁ where M₁ is a total area of thetest keys formed on the free area A₁. The total area M₁ of the test keysis limited such that R₁ is less than about 10%. Similarly, measurementratio R_(S) is defined by the equation R_(S)=M_(S)/A_(S), where M_(S) isa total area of the test keys formed on the free area A_(S). R_(S) islimited to a value less than 10% by limiting the test key area M₁.

In another embodiment of the invention, a fabrication method for asemiconductor wafer with free areas restricting test key placementcomprises the following steps. A semiconductor wafer is provided with atleast a first and second scribe line, in which at least one corner pointof a main area of a die is defined by the intersection of the firstscribe line and the second scribe line. At least one “free area” is thenformed on the first scribe line adjacent to the corner point of the die.The free area A₁ is defined by the equation A₁=D₁×S₁, where D₁ is thedistance from the corner point of the die extending toward the main areaof the die, and S₁ is the width of the first scribe line. The die isthen separated using a cutting method for separating the dies along thefirst scribe line and the second scribe line. Both the first scribe lineand the second scribe line are defined by the multi-layer structure, andat least one layer of the multi-layer structure is a low-k dielectriclayer.

The dies on the wafer may be separated by any suitable method includingdiamond sawing, laser cutting, liquid jet scribing, water jet cutting orany combination of these cutting methods. The low-k dielectric layer hasa dielectric constant less than approximately 3.5 and preferably lessthan 3.0. The “free area” is preferably defined on the top layer of themulti-layer structure of the first scribe line. Similar to the abovediscussion, if test keys are to be formed on the first scribe line, thesecond scribe line or the combination thereof, the area of the test keysshould meet the measurement ratio R₁. As discussed above, themeasurement ratio R₁ is defined by the equation R₁=M₁/A₁, where M₁ is atotal area of the test keys formed on the free area A₁. Also asdiscussed above, M₁ is limited such that R₁ is less than 10%. Likewise,the measurement ratio R_(S) is defined by the equationR_(S)=M_(S)/A_(S), where M_(S) is a total area of the test keys formedon the free area A_(S) and M_(S) is limited so that R_(S) is less than10%.

In another embodiment of the invention, a semiconductor wafer includes aconductive ring with an array of apertures such as slots or holes. A diehas a main area comprising a multi-layer structure, and at least onelayer of the multi-layer structure is a low-k dielectric layer. A firstperipheral region is defined along a first direction of the main area ofthe die, a second peripheral region is defined along a second directionof the main area of the die, and a corner area is defined by theintersection of the first peripheral region and the second peripheralregion. A portion of a conductive ring surrounding the die is formed inthe area of the die and adjacent the first peripheral region and thesecond peripheral region. An array of apertures, such as one or moreslots or one or more lines of holes, is formed in the conductive ringand adjacent the corner area of the main area of the die.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawing, in which:

FIG. 1 is a top view of a wafer with dies separated by scribe linesaccording to an embodiment of the present invention;

FIG. 2 is a cross-section illustrating the multi-layer structure of thewafer;

FIG. 3A is a top view illustrating a free area restricting test keyplacement on a scribe line adjacent one die according to one embodimentof the present invention;

FIG. 3B is a top view illustrating a free area restricting test keyplacement on a scribe line adjacent one die according to anotherembodiment of the present invention;

FIG. 3C is a top view illustrating a free area restricting test keyplacement on a scribe line adjacent one die according to still anotherembodiment of the present invention;

FIG. 3D is a top view illustrating a free area restricting test keyplacement on a scribe line adjacent one die according to yet anotherembodiment of the present invention;

FIG. 4 is a top view illustrating a free area restricting test keyplacement on a scribe line adjacent one die according to one moreembodiment of the present invention;

FIG. 5 is a top view illustrating free areas restricting test keyplacement on a scribe line adjacent four dies according to anotherembodiment of the present invention;

FIG. 6 is a top view illustrating free areas restricting test keyplacement on a scribe line adjacent four dies according to anotherembodiment of the present invention;

FIG. 7 is a top view of a main area of a die having a pair of slotsdefined in a guard ring surrounding the die according to the presentinvention;

FIG. 8 is a cross-section along line 8-8 of FIG. 7;

FIG. 9 is a top view similar to FIG. 7 except it shows rows of holesformed in the guard ring; and

FIGS. 10A–10C are top views of another embodiment of the inventionshowing an array of slots in the guard ring combined with the test keydesign rule on a scribe line as disclosed in FIGS. 3A–6.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of embodiments of the present invention arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

According to one embodiment of the present invention, a semiconductorwafer is provided with “free areas” that restrict the placement of testkeys on scribe lines. This limitation or restriction reducesdelamination or peeling near the die corners. The “free areas” locatedon the scribe lines may be used with an LK wafer (low-k wafer).Particularly, the phrase “free areas” restricting test key placementmeans that a limited arrangement of test keys may be placed or locatedin the “free area.” That is, a few test keys can be located on the freearea if a measurement ratio of the test key area to the free areasatisfies or falls within an acceptable range. Alternately, a “freearea” may be so restricted that no test keys at all are permitted.

FIG. 1 is a top view of a wafer with dies separated by scribe linesaccording to one embodiment of the present invention. The semiconductorwafer 10 comprises substantially isolated dies (or chips) 16 separatedfrom each other by first scribe lines 12 and second scribe lines 14. Thefirst scribe lines 12 extend along a first direction and the secondscribe lines 14 extend along a second direction, in which theintersection of one of the first scribe lines and one of the secondscribe lines define at least one corner point of a die 16. For example,in the illustrated embodiment, one of the first scribe lines 12 extendalong a horizontal direction, and the second scribe lines 14 extendalong a vertical direction, such that their intersection defines cornerpoints of four of the dies 16. Also, the semiconductor wafer 10comprises test keys 18 located on the scribe lines 12 and 14, except forthe restricted or “free areas” described below. Typically, thesemiconductor wafer 10 will be an LK (low-k dielectric) wafer, and eachof the scribe lines 12 and 14 are defined by the multi-layer structure.

FIG. 2 is a cross-section illustrating the multi-layer structure of thewafer including the area of the wafer with the scribe lines. Each of thescribe lines 12 and 14 are formed as part of the multi-layer structure24 formed on a substrate 20. The substrate 20 may be fabricated usingbulk Si, SOI, SiGe, GaAs, InP, or other semiconductor materials. Themulti-layer structure 24 comprises layers 21, 22, and 23. At least oneof the layers 21, 22, and/or 23 will typically be a low-k dielectriclayer of a dielectric constant (k) lower than approximately 3.5, andpreferably lower than 3.0. For example, the low-k dielectric layer maybe CVD SiOC, CVD SiOCN, Spin-on SiOC, CVD polymer, Spin-on polymer, FSG,or SiO₂.

The free areas described below represent at least one layer of themulti-layer structure 24 in the area of the scribe lines 12 or 14.Preferably, the free areas are defined on the top of the multi-layerstructure 24. Alternatively, the free areas can be defined on at leastone of the top three layers of the multi-layer structure 24.

The individual dies 16 containing circuitry and formed on wafer 10 areseparated by suitable cutting methods, such as diamond sawing, lasercutting, liquid jet scribing (such as water jet cutting) or acombination of these cutting methods. The test key 18 may be anauxiliary conductive structure, an electrically activated structure(such as PCM), or a non-electrically activated structure (such as aframe cell).

Examples of the free area that restrict test key placement on the scribelines 12 and 14 adjacent one corner point of the individual die 16 aredescribed below.

FIG. 3A is a top view illustrating a free area restricting test keyplacement on the scribe lines adjacent one die according to anembodiment of the present invention. The first scribe line 12 extendingalong the first direction intersects the second scribe line 14 extendingalong the second direction to separate a main area 26 of one of the dies16. The main area 26 with circuit elements formed thereon has a cornerpoint P defined by the intersection of the first scribe line 12 and thesecond scribe line 14. Also, depending on the test key design rule, testkeys 18 may be formed without restriction on the first scribe line 12 orthe second scribe line 14, except for the free area A₁ near the cornerpoint P. The free area A₁ is on the first scribe line 12 adjacent to thecorner point P. The free area A₁ is defined by the equation A₁=D₁×S₁,where D₁ is a distance from the corner point P toward the main area 26,and S₁ is the width of the first scribe line 12. Preferably, D₁ is lessthan 600 μm, and S₁ is greater than 20 μm

The free area A₁ is on at least one layer of the multi-layer structure24 of the first scribe line 12. Preferably, the free area A₁ is on thetop of the multi-layer structure 24. Alternatively, the free area A₁ ison at least one of the top three layers of the multi-layer structure 24.

Although test keys 18 could be completely prohibited from area A₁,preferably a few test keys 18 are permitted on the free area A₁ if themeasurement ratio R₁ is less than about 10%. R₁ is defined by theequation R₁=M₁/A₁ where M₁ is the total area of the test keys 18 formedon the free area A₁.

FIG. 3B is a top view illustrating a second example of a free area thatrestricts test key placement on the scribe lines adjacent one die.Elements similar to those shown in FIG. 3A are omitted here.

Similar to the above discussion, the test keys 18 are formed on thefirst scribe line 12 or the second scribe line 14 without restriction,except for free area A₂ near the corner point P. The free area A₂ is onthe second scribe line 14 adjacent to the corner point P. The free areaA₂ is defined by the equation A₂=D₂×S₂, where D₂ is a second distancefrom the corner point P toward the main area 26, and S₂ is the width ofthe second scribe line 14. Preferably, D₂ is less than 600 μm, and S₂ isgreater than 20 μm.

The free area A₂ is on at least one layer of the multi-layer structure24 of the second scribe line 14. Preferably, the free area A₂ is on thetop of the multi-layer structure 24. Alternatively, the free area A₂ ison at least one of the top three layers of the multi-layer structure 24.As discussed above with respect to the example of FIG. 3A, it is oftenpreferable to also allow the formation of a few test keys 18 on the freearea A₂ if the measurement ratio R₂ is less than 10%. Similar to theembodiment discussed above, R₂ is defined by the equation R₂=M₂/A₂,where M₂ is the total area of the test keys 18 formed on the free areaA₂.

FIG. 3C is a top view illustrating a third example of a free area thatrestricts test key placement on the scribe lines adjacent one die.Elements similar to those in FIGS. 3A and 3B are omitted here.

Depending on the test key design rule, the test keys 18 are formedwithout restriction on the first scribe line 12 or the second scribeline 14, except for a free area A_(S) near the corner point P. The freearea A_(S) is on the intersection of the first scribe line 12 and thesecond scribe line 14 adjacent the corner point P. The free area A_(S)is defined by the equation A_(S)=S₁×S₂, where S₁ is the width of thefirst scribe line 12, and S₂ is the width of the second scribe line 14.Preferably, S₁ is greater than about 20 μm and S₂ is greater than about20 μm<S₂.

The free area A_(S) is on at least one layer of the multi-layerstructure 24. Preferably, the free area A_(S) is on the top of themulti-layer structure 24. Alternatively, the free area A_(S) is on atleast one of the top three layers of the multi-layer structure 24. Also,as discussed above with respect to FIGS. 3A and 3B, it is preferable toallow the formation of a few test keys 18 on the free area A_(S) if themeasurement ratio R_(S) is no greater than 10%. R_(S) is defined by theequation R_(S)=M_(S)/A_(S), where M_(S) is the total area of the testkeys 18 formed on the free area A_(S).

FIG. 3D is a top view illustrating a fourth example of free areas thatrestrict test key placement on the scribe lines adjacent one die.Elements similar to those found in FIGS. 3A through 3C are omitted here.

Depending on the test key design rule, the test keys 18 are formed onthe first scribe line 12 or the second scribe line 14, except for thefree areas A₁, A₂, and A_(S) near the corner point P. Also, as discussedabove, it is often preferable to allow the formation of a few test keys18 on the free areas A₁, A₂, and A_(S) if the measurement ratio R isless than 10%. R is defined by the equationR=(M₁+M₂+M_(S))/(A₁+A₂+A_(S)).

A free area that restricts test key placement on the scribe linesadjacent four corners of the individual die is described below withrespect to FIG. 4.

A pair of first scribe lines 12I and 12II and a pair of second scribelines 14I and 14II separate the die 16 and define four corner points Pof the main area 26. Also, depending on the test key design rule, testkeys 18 are formed without restriction on the first scribe lines 12I and12II and the second scribe lines 14I and 14II adjacent the die 16,except for free areas A₁, A₂, A_(S) near the four corner points P.

The free areas restricting test key placement on the scribe linesadjacent four dies are described below.

FIG. 5 is a top view illustrating a sixth example of free areasrestricting test key placement on the scribe lines adjacent to fourdies.

Four of the individual dies 16I, 16II, 16III, and 16IV are separatedfrom each other by a first scribe line 12 and a second scribe line 14,in which corner points P₁, P₂, P₃, P₄ of the four dies 16I, 16II, 16III,and 16IV respectively define the intersection of the first scribe line12 and the second scribe line 14. Also, depending on the test key designrule, test keys 18 are formed without restriction on the first scribeline 12 and the second scribe line 14 adjacent the dies 16I, 16II,16III, and 16IV, except for free areas A₁, A₂, A₃, A₄, and A_(S)adjacent the four corner points P₁, P₂, P₃, P₄ of the dies 16I, 16II,16III, and 16IV.

The free area A₁ is on the first scribe line 12 between the first die16I and the third die 16III adjacent the corner points P₁ and P₃. Thefree area A₁ is defined by the equation A₁=D₁×S₁, where D₁ is a firstdistance from the corner point P₁ of the first die 16I toward the mainarea of the first die 16I, and S₁ is the width of the first scribe line12. Preferably, D₁ is less than 600 μm and S₁ is greater than 20 μm. Alimited number of keys 18 may be formed in the area A₁ so long as themeasurement ratio R₁ is less than about 10%. R₁ is defined by theequation R₁=M₁/A₁, where M₁ is the total area of the test keys 18 formedon the free area A₁.

The free area A₂ is on the second scribe line 14 between the first die16I and the second die 16II adjacent the corner points P₁ and P₂. Thefree area A₂ is defined by the equation A₂=D₂×S₂, where D₂ is a seconddistance from the corner point P₂ of the second die 16II toward the mainarea of the second die 16II, and S₂ is the width of the second scribeline 14. Preferably, D₂ is less than 600 μm, and S₂ is greater than 20μm. As was the case for the free area A₁, a limited number of test keys18 may be formed in the area A₂ so long as the measurement ratio R₂ isless than 10%. Similar to the above discussions, R₂ is defined by theequation R₂=M₂/A₂, where M₂ is the total area of the test keys 18 formedon the free area A₂.

The free area A₃ is on the second scribe line 14 between the third die16III and the fourth die 16IV adjacent the corner points P₃ and P₄. Thefree area A₃ is defined by the equation: A₃=D₃×S₂, where D₃ is thedistance from the corner point P₃ of the third die 16III toward the mainarea of the third die 16III. Preferably, D₂ is less than 600 μm, and S₂is greater than 20 μm. As discussed above with respect to areas A₁ andA₂, a limited number of test keys 18 can be formed in area A₃ so long asthe measurement ratio R₃ is less than 10%. R₃ is defined by the equationR₃=M₃/A₃, where M₃ is the total area of the test keys 18 formed on thefree area A₃.

The free area A₄ is on the first scribe line 12 between the second die16II and the fourth die 16IV adjacent the corner points P₂ and P₄. Thefree area A₄ is defined by the equation: A₄=D₄×S₁, where D₄ is thedistance from the corner point P₄ of the fourth die 16IV toward the mainarea of the fourth die 16IV. Preferably, D₄ is less than 600 μm. Again,if test keys are to be formed in area A₄, the measurement ratio R₄ mustbe less than about 10%. As before, R4 is defined by the equationR₄=M₄/A₄, where M₄ is the total area of the test keys 18 formed on thefree area A₄.

The free area A_(S) is on the intersection of the first scribe line 12and the second scribe line 14 adjacent the corner points P₁, P₂, P₃ andP₄. The free area A_(S) is defined by the equation: A_(S)=S₁×S₂, whereS₁ is the width of the first scribe line 12, and S₂ is a width of thesecond scribe line 14. Preferably, S₁ is greater than 20 μm, and S₂ isalso greater than 20 μm. As discussed above, test keys formed in areaA_(S) must be limited such that the measurement ratio R_(S) is less than10%. R_(S) is defined by the equation R_(S)=M_(S)/A_(S), where M_(S) isthe total area of the test keys 18 formed on the free area A_(S).

In addition, each of the free areas A₁, A₂, A₃, A₄, and A_(S) is on atleast one layer of the multi-layer structure 24 of the scribe line 12 or14. Preferably, each of the free areas A₁, A₂, A₃, A₄, and A_(S) is onthe top of the multi-layer structure 24. Alternatively, each of the freeareas A₁, A₂, A₃, A₄ and A_(S) is on at least one of the top threelayers of the multi-layer structure 24.

FIG. 6 is a top view illustrating free areas prohibiting test keyplacement on the scribe lines adjacent four dies according to yetanother example of the present invention. Elements similar to thosedescribed in FIG. 5 are omitted here.

The free areas A₁, A₂, A₃, A₄, and A_(S) are asymmetrical patterns, inwhich D₁≠D₄, and D₂≠D₃.

In comparison with the conventional art, the several examples of thepresent invention provide free areas restricting test key placement onthe scribe lines to prevent peeling near the test keys at the diecorners from stress exerted during the sawing process, thus avoidingdelamination at the interface between the multi-layers at the diecorners. The free areas restricting test key placement on the scribelines ensure reliability of the IC device.

Another embodiment of the present invention provides a conductivestructure that encloses a main area of a die. The conductive structuredefines an array of apertures at the corner of the die in order toprevent the die from being cracked by stresses exerted at the corners ofa die. The use of the apertures in the conductive structure isparticularly effective to prevent cracks in wafers using low-kmaterials. Moreover, the conductive structure with the array ofapertures can be combined with the free areas restricting test keyplacement to achieve the advantages of both.

FIG. 7 is a top view of a main area of a die having an array ofapertures according to the present invention. Elements similar to thosediscussed with respect to the earlier figures are omitted here.

The main area 26 of the die 16 is defined by the intersection of thefirst scribe line 12 and the second scribe line 14. The main area 26includes a first peripheral region 27I defined along the firstdirection, a second peripheral region 27II defined along the seconddirection, and a corner area 29 defined by the intersection of the firstperipheral region 27I and the second peripheral region 27II. Aconductive structure or “ring” 28 is formed on the main area 26 andextends adjacent the first peripheral region 27I and the secondperipheral region 27II. It is noted that the phrase “conductive ring” asused herein is intended to cover rectangular or square shaped seals aswell as round seals. An array of apertures, such as one or more slots30, is formed in the conductive ring 28 and adjacent to the corner area29. Moreover, circuit elements and wirings are formed on the circuitarea 32, which is enclosed by the conductive ring 28. The conductivering 28 is electrically connected to the circuit elements to apply apower source or a ground potential for circuit elements on the encloseddie. Preferably, a width W of the conductive ring 28 is approximately20–350 μm. In addition, a plurality of bonding pads 33 is formed outsidethe conductive ring 28 and on the first peripheral region 27I and thesecond peripheral region 27II.

The main area 26 of the die 16 may be formed on an LK (low-k dielectric)wafer, and the corner area 29 is part of the multi-layer structure. FIG.8 is a cross-section along line 8-8 of FIG. 7 illustrating the pair ofslots 30. In the main area 26, the conductive ring 28 with the slots 30is formed on a multi-layer structure 24 of a substrate 20. Themulti-layer structure 24 comprises layers 21, 22, and 23. Preferably, atleast one of the layers 21, 22, and/or 23 is a low-k dielectric layer ofa dielectric constant (k) lower than approximately 3.5 and preferablylower than about 3.0. For example, the low-k dielectric layer may be CVDSiOC, CVD SiOCN, Spin-on SiOC, CVD polymer, Spin-on polymer, FSG, orSiO₂.

FIG. 8 is a top view illustrating one example of a suitable array ofapertures. According to this embodiment, the array of aperturescomprises a pair of slots 30 located at the corner of the die 32. Atleast one portion of a slot extends parallel to the first direction orthe second direction. According to the illustration of FIG. 8, the arrayof apertures comprises a pair of slots having an L-shape formed in theconductive ring 28 at the corner portion of the die 32. As shown, theapertures comprise at least two L-shaped slots 30 formed in the cornerportion of the conductive ring 28.

FIG. 9 is a top view of another example of an array of apertures in theconductive ring 28. The array of apertures comprises two rows of holesin the corner portion of the conductive ring 28. Furthermore, the arrayof holes may extend only parallel to one of the first peripheral region27I or the second peripheral region 27II. Alternately, the two rows ofholes may be L-shaped as shown in FIG. 9.

FIGS. 10A–10C are top views of other examples of the conductive ring 28with apertures combined with the design rule for restricting theplacement of test keys on a scribe line as described above. Elementssimilar to those found in FIGS. 3A–3C and FIG. 7 are omitted here.

Depending on the test key design rule, the test keys 18 are formedwithout restriction on the first scribe line 12 or the second scribeline 14, except for the free areas A₁, A₂, and A_(S) near the cornerpoint P of the main area 26.

In FIG. 10A, test keys 18 are formed on the first scribe line 12 or thesecond scribe line 14, except for a free area A₁ near the corner pointP. The free area A₁ is on the first scribe line 12 adjacent to thecorner point P. The free area A₁ is defined by the equation A₁=D₁×S₁.Moreover, a few test keys 18 may be formed on the free area A₁ if themeasurement ratio R₁ is less than about 10%. R1 is defined by theequation R₁=M₁/A₁, where M₁ is the total area of the test keys 18 formedon the free area A₁.

In FIG. 10B, test keys 18 are formed without restriction on the firstscribe line 12 or the second scribe line 14, except for on a free areaA₂ near the corner point P. The free area A₂ is on the second scribeline 14 adjacent to the corner point P. The free area A₂ is defined bythe equation A₂=D₂×S₂. Moreover, a few test keys 18 may be formed on thefree area A₂ if the measurement ratio R₂ is less than 10%. R₂ is definedby equation R₂=M₂/A₂, where M₂ is the total area of the test keys 18formed on the free area A₂.

In FIG. 10C, test keys 18 are formed without restriction on the firstscribe line 12 or the second scribe line 14, except for a free areaA_(S) near the corner point P. The free area A_(S) is on theintersection of the first scribe line 12 and the second scribe line 14adjacent the corner point P. The free area A_(S) is defined by theequation A_(S)=S₁×S₂. Moreover, a few test keys 18 can be formed on thefree area A_(S) if the measurement ratio R₂ is less than 10%. R₂ isdefined by the equation R_(S)=M_(S)/A_(S), where M_(S) is the total areaof the test keys 18 formed on the free area A_(S).

Although the present invention and its advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the invention as defined by the appended claims.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, manufacture,means, methods and steps described in the specification. As one ofordinary skill in the art will readily appreciate from the disclosure ofthe present invention, processes, machines, manufacture, compositions ofmatter, means, methods, or steps, presently existing or later to bedeveloped, that perform substantially the same function or achievesubstantially the same result as the corresponding embodiments describedherein may be utilized according to the present invention. Accordingly,the appended claims are intended to include within their scope suchprocesses, manufacture, means, methods, or steps.

1. A multi-layer semiconductor wafer structure defining a multiplicityof dies formed thereon, said wafer structure comprising: a first scribeline having a selected width extending along a first direction; a secondscribe line having a selected width extending along a second directionand intersecting said first scribe line; four dies located at andseparated by the intersection of said first and second scribe lineswherein each of the four dies comprises a corner point adjacent theintersection of said first and second scribe lines; a first free area A₁on the first scribe line adjacent the corner point of the first die,wherein A₁ is defined by the equation A₁=D₁×S₁, and wherein D₁ is thedistance extending from the corner point of the first die, and S₁ is thewidth of the first scribe line; a second free area A₂ on the secondscribe line adjacent the corner point of the second die, wherein A₂ isdefined by the equation A₂=D₂×S₂, and wherein D₂ is the distance fromthe corner point of the second die, and S₂ is the width of the secondscribe line; a third free area A₃ on the second scribe line adjacent thethird corner point of the third die, wherein A₃ is defined by theequation A₃=D₃×S₂, and wherein D₃ is the distance from the corner pointof the third die; a fourth free area A₄ on the first scribe lineadjacent the corner point of the fourth die, wherein A₄ is defined bythe equation A₄=D₄×S₁, and wherein D₄ is the distance from the cornerpoint of the fourth die; and a fifth free area A_(S) on the intersectionof the first scribe line and the second scribe line and is defined bythe equation A_(S)=S₁×S₂.
 2. The semiconductor wafer of claim 1 furthercomprising: at least one test key formed on at least one of the freeareas A₁, A₂, A₃, A₄ and A_(S); wherein a first measurement ratio R₁ isdefined as the equation R₁=M₁/A₁, wherein M₁ is the total area of thetest keys formed on the first free area A₁; wherein a second measurementratio R₂ is defined as the equation: R₂=M₂/A₂, wherein M₂ is the totalarea of the test keys formed on the second free area A₂; wherein a thirdmeasurement ratio R₃ is defined as the equation: R₃=M₃/A₃, wherein M₃ isthe total area of the test keys formed on the third free area A₃;wherein a fourth, measurement ratio R₄ is defined as the equation: R₄=M₄/A₄, wherein M₄ is the total area of die test keys formed on thefourth free area A₄; wherein a fifth measurement ratio R_(S) is definedas the equation: R_(S)=M_(S)/A_(S), wherein M_(S) is the total area ofthe test keys formed on the fifth free area A_(S); and wherein a totalmeasurement ration R is defined as the equation R=(M₁×M₂×M₃×M₄×M_(S))/(A₁×A₂×A₃×A₄×A_(S)).
 3. The semiconductor wafer of claim 2 wherein thefirst measurement ratio R₁, is less than about 10%.
 4. The semiconductorwafer of claim 1 wherein the distance D₄ is less than about 600 μm. 5.The semiconductor wafer of claim 1 wherein the width S₁ of the firstscribe line is greater than about 20 μm.
 6. The semiconductor wafer ofclaim 1 wherein the width S₂ of the second scribe line is greater thanabout 20 μm.
 7. The semiconductor wafer of claim 1 wherein themulti-layer structure is formed on a substrate selected front the groupconsisting of bulk Si, SOI, SiGe, GaAs and InP.
 8. The semiconductorwafer of claim 1 wherein each of said four dies comprises: a firstperipheral region parallel to said first scribe line; a secondperipheral region parallel to said second scribe line; a conductive ringformed between said die and said first peripheral region and said secondperipheral region; and an array of apertures formed in the conductivering arid adjacent the corner area of the die.
 9. The semiconductorwafer of claim 1 wherein at least one layer of the multilayered waferstructure is a low-k dielectric layer-having a dielectric constant lessthan approximately 3.5.
 10. The semiconductor wafer of claim 8 whereinthe array of apertures comprises two rows of holes.
 11. Thesemiconductor wafer of claim 9 wherein said array of apertures comprisesat least two slots.
 12. The semiconductor wafer of claim 8 wherein thearray of apertures extends along at least one of the first peripheralregion and the second peripheral region.
 13. The semiconductor wafer ofclaim 8, wherein each of the four dies further comprises a circuit areawith a plurality of circuit elements, wherein the conductive ring iselectrically connected to the circuit elements to apply one of a powersource and a ground potential to the circuit elements.
 14. Thesemiconductor wafer of claim 8 wherein the conductive ring has a widthof between about 50 μm and 300 μm.